The present applicant has already proposed an internal combustion engine which has a collision surface formed at the center portion of a cavity formed in the top surface of the piston, has the fuel injected from the fuel injector strike the collision surface to disperse from the collision surface in the circumferential directions in the cavity, then has the dispersed fuel ignited by a spark plug or glow plug (see Japanese Unexamined Patent Publication (Kokai) No. 63-120815). In such an internal combustion engine, the spark plug or glow plug is used to ignite the fuel, but later studies showed that if the method of formation of a fuel spray using such a collision action is applied to a compression-ignition internal combustion engine, the ignition lag time becomes extremely short and therefore combustion with a gentle rise in pressure can be obtained. Therefore, the present applicant has also applied for a patent for such a compression-ignition internal combustion engine as well (PCT/JP90/00718). In this compression-ignition internal combustion engine, substantially all the injected fuel is made to burn in the cavity formed at the top surface of the piston in the same way as a general compression-ignition internal combustion engine.
A cavity formed in the top surface of a piston inherently has a volume able to accommodate an amount of air sufficient for burning all the injected fuel and therefore if all the air in the cavity can be used for the combustion, then excellent combustion can be obtained even if substantially all of the injected fuel is made to burn in the cavity of the piston as mentioned above. To use all of the air in the cavity for the combustion, however, the injected fuel must be distributed uniformly in the cavity as a whole. Nevertheless, to cause the injected fuel to uniformly distribute in the cavity as a whole is difficult for a general compression-ignition internal combustion engine, of course, and even more so for a compression-ignition internal combustion engine where the injected fuel is made to collide with a collision surface. Therefore, there is the problem that if substantially all of the injected fuel is made to burn in the cavity of the piston, the rate of utilization of the air becomes insufficient and therefore a large amount of unburned hydrocarbons and smoke is generated.